1. Field of the Invention
Embodiments of the present invention relate to methods and devices for closing a body lumen or cavity and, in particular, for closing a patent foramen ovale.
2. Description of the Related Art
Embolic stroke is the nation's third leading killer for adults, and is a major cause of disability. There are over 700,000 strokes per year in the United States alone. Of these, roughly 100,000 are hemorrhagic, and 600,000 are ischemic (either due to vessel narrowing or to embolism). About 50,000 of the ischemic strokes are believed to be caused by a patent foramen ovale. However, the risk of recurrent stroke is higher in patients whose strokes are caused by a patent foramen ovale.
Pharmacological therapies for stroke prevention such as oral or systemic administration of warfarin or the like have been inadequate due to serious side effects of the medications and lack of patient compliance in taking the medication.
In general, the heart is divided into four chambers, the two upper being the left and right atria and the two lower being the left and right ventricles. The atria are separated from each other by a muscular wall, the interatrial septum, and the ventricles by the interventricular septum.
Either congenitally or by acquisition, abnormal openings, holes or shunts can occur between the chambers of the heart or the great vessels (interatrial and interventricular septal defects or patent ductus arteriosus and aortico-pulmonary window respectively), causing shunting of blood through the opening. A patent foramen ovale is a condition wherein an abnormal opening is present in the septal wall between the two atria of the heart. Blood can flow directly between these two atria, compromising the normal flow of blood and efficiency of the patient's heart. The deformity is usually congenital, resulting from a failure of completion of the formation of the septum, or wall, between the two sides during fetal life when the heart forms from a folded tube into a four-chambered, two unit system.
In contrast to other septal defects which tend to have a generally longitudinal axis, a patent foramen ovale tends to behave like a flap valve. Accordingly, the axis of the patent foramen ovale tends to be at an angle, and almost parallel to the septal wall.
These deformities can carry significant sequelae. For example, with a patent foramen ovale, blood is shunted from the left atrium of the heart to the right, producing an over-load of the right heart. In addition to left-to-right shunts such as also occur in patent foramen ovale, the left side of the heart has to work harder because some of the blood which it pumps will recirculate through the lungs instead of going out to the rest of the body. The ill effects of these defects usually cause added strain on the heart with ultimate failure if not corrected.
Previously, patent foramen ovale have required relatively extensive surgical techniques for correction. To date the most common method for closing intracardiac shunts, such as a patent foramen ovale, entails the relatively drastic technique of open-heart surgery, requiring opening the chest or sternum and diverting the blood from the heart with the use of a cardiopulmonary bypass. The heart is then opened, the defect is sewn shut by direct suturing with or without a patch of synthetic material (usually of Dacron, Teflon, silk, nylon or pericardium), and then the heart is closed. The patient is then taken off the cardiopulmonary bypass machine, and the chest is closed.
In place of direct suturing, closures of a patent foramen ovale by means of a mechanical prosthesis have also been disclosed. A number of these devices, designed for closures of interauricular septal defects, have been used to correct patent foramen ovale.
Although these devices have been known to effectively close other septal defects, there are few closure devices which have been developed specifically for closing patent foramen ovale. Although these devices have been effective in some cases, there is still much room for improvement.
Notwithstanding the foregoing, there remains a need for a method and improved apparatus for correcting patent foramen ovale.